Is there a hard reset deep within the unit?

MY Go 500 was working happily then suddenly I had a spinning wheel on the display which only stopped when I removed the power and allowed the battery to discharge. On reboot (drumroll) it got part way in and then just died.

Now I have a blank screen, no signs of life and have tried all of the recharge/hold power button for 90 seconds sequences.

Opened it up hoping to find an obvious means of resetting the hardware but nothing obvious. battery is now recharged externally but no change. Tried shorting some caps to discharge them in the hope that it might help but no result.